The embodiments of the present invention relate to a color management technology, in particular to a color management method and device.
With the widely usage of various newly emerging input/output devices for digital color image, such as color scanner, digital camera, display device, color printer, etc., a color distortion issue during the transmission and duplicating reproduction among various devices for color image increasingly causes attention.
To solve the distortion issue when the color information is transferred among different devices, it has been proposed a Color Management Module (CMM) technology to correct the image data according to the color reproduction characteristic of respective image device, CMM technology is a technology to perform color conversion from a color space of a source device to a color space of any target device, for accurately transferring color. The currently available CMM products mainly are: “Adobe CMM”, “Agfa CMM”, “Apple CMM”, “Heidelberg CMM”, “Imation CMM”, “Kodak CMM” and “X-Rite CMM” etc. The content of color management comprises device calibration, characteristic description and color conversion. Device calibration is precondition to ensure the normal operation of a system; the description of the device characteristic is the description for the color expression ability and the rendered color range of different devices; the color conversion is to convert a color space of one device into a color space of another device under the identical condition, to build a corresponding color mapping among different color spaces.
The color space could be classified as three categories: Red Green Blue (RGB) type of color space/computer graphic color space, which is mainly used for color display system of television (TV) and computer, for example, color spaces such as “HIS”, “HSL”, and “HSV” and so on. The standard Red Green Blue (sRGB) color space, which is a standard RGB color space, is used for color data standardized exchange in multimedia systems and devices such as computer, internet and so on. “XYZ” type of color space/International Commission on Illumination (CIE) color space is a color space independently of the device, for example, color spaces as “CIE 1931 XYZ”, “L*a*b”, “L*u*v” and “LCH” and so on. “YUV” type of color space/TV system color space could effectively transfer color TV image by compressing chroma information, such as color spaces as “YUV”, “YIQ” and “SMPTE-240M Y′PbPr” etc., while “YUV” color space and “YIQ” color space are used in the TV signals of Phase Alternating Line (PAL) and National Television Standards Committee (NTSC) TV system, respectively.
FIG. 1 is a color gamut comparison graph of three principal colors Light Emitting Diode (LED) backlight with sRGB color space and “YIQ” color space of NTSC TV system. The color gamut is color expression capability, which is also the color range contained in color space. The abscissa represents red (X), the ordinate represents green (Y), wherein VA represents a visual area of human eyes, sRGB represents a sRGB color space used for multimedia systems and devices such as computer, internet and so on, RGB LED represents the color gamut of three principal colors LED backlight, NTSC represents the “YIQ” color space of NTSC TV system. As can be seen from FIG. 1, the color gamut of three principal colors LED backlight is far beyond that of sRGB color space and “YIQ” color space of NTSC TV system.
In order to convert the color space of input image signal into the color space of the display device so as to render the color in the display device, the provided color management methods in the existing art include a conventional look-up table method or a neural network algorithm. For example, the conversion computation from sRGB, “YUV” or “YIQ” color space and so on to the RGB color space of the display device is achieved by using “a tone matrix model” or “a matrix look-up table model”, and then the colors are rendered based on the RGB values of the color space of the display device.
In the process of implementing the embodiments of the present invention, the inventor has found at least the following problems existing in the prior art: currently the color gamut of three principal colors LED backlight is far beyond that of sRGB color space, “YIQ” color space, “YUV” color space and so on, and when the color gamut of input color signal is less than that of the display device reproducing said color signal, the color expression capability of the display device could not be fully utilized, at the same time, it makes the errors occur between the color space of the input color signal and that of the display device during a match process therebetween. Thus in a regular three principal colors LED backlight TV, it is always found a problem that the color is over bright, which in the distortion in red area is particularly more severe, which causes not accurately reproducing the color.